This invention relates to a composition and process for enhancing subsequent soil removal from fabrics. More particularly it relates to a composition and process whereby subsequent removal of oily soil and stains from fabrics woven from polyester fibers, and from fabrics which employ combinations of polyester fibers and other fibers (e.g. 65% polyester, 35% cotton blends), is enhanced by applying to said fabrics, in an aqueous solution, a soil release agent which imparts hydrophilic character to the polyester fiber, said solution having an acid pH. As used herein, the term "solution" refers to dispersion as well as true solution.
As is well known in the art, fabrics which are woven from polyester fibers, the most common of which being copolymers of ethylene glycol and terephthalic acid, and being sold under a number of trade names, e.g., Dacron, Fortrel, Kodel and Blue C Polyester, tend to be quite hydrophobic. The hydrophobic character of these fabrics prevents or reduces the ability of water to wet the fabric, which is necessary to remove oily soil and oily stains during the washing process. Since the inherent character of the fabric itself is hydrophobic, or oleophilic, once an oily soil or oily stain is deposited on the fabric, either by normal use or by accident, the oily soil or oily stain tends to be "attached" to the surface of the fiber, and as a result the oily soil or stain is difficult to remove in the laundering process. Other fabrics such as cotton can be dirtied by oily stains or oily soil in the same manner as polyester fabrics. However, because cotton fibers are more hydrophilic in nature than polyester fibers, oily stains and oily soil are more easily removed from cotton fabrics, due to a greater affinity of the fabric for water. This difference in hydrophilic/hydrophobic character is due in part to the basic building blocks of the fibers themselves, i.e., since polyester fibers are copolymers of terephthalic acid and ethylene glycol, they have less affinity for water because there are fewer free hydrophilic groups, e.g., hydroxyl or carboxyl groups where hydrogen bonding can occur, than is the situation with cotton which is a cellulose derivative containing a large number of hydrophilic groups which are compatible with and have affinity for water.
As a result of cotton's hydrophilic nature, when an oily soil stain is present in a cotton fabric which is laundered, the soil tends to "ball-up" into a droplet on contact with water just as oil droplets form on the surface of an oil/water mixture. Through the mechanical action of washing and the action of synthetic detergents and builders normally used in the washing step of the laundering process, this droplet is removed from the fabric. This is in contrast to the situation which exists with a polyester fiber in that water does not "wick" through the fabric as well and thus the oily soil or stain tends to be retained throughout the fabric because of the inherent hydrophobic character of the fabric and the lack of affinity of oily soils for water.
Because of the fact that polyester and polyester-blend fabrics (e.g. polyester-cotton blends) are susceptible to oily staining, and the fact that once stained the fabric is difficult to clean, manufacturers of polyester fibers and of polyester fabrics and blends have sought to increase the hydrophilic character of the polyester so that on laundering the fabric will be easily cleaned.
A number of approaches toward building more hydrophilic character into polyester fabrics and fabrics which are blends of cotton fibers and polyester fibers have been taken. All of these approaches involve a proces applied by the textile-fiber manufacturer or the textile manufacturer. Netherlands Application 65/09456 [see also D. A. Garrett and P. N. Hartley, I. Soc. Dyers and Colourists, 82, 7, 252-7 (1967) and Chem. Eng. News, 44, 42-43 (Oct. 17, 1966)] describes the treatment of polyester fabrics in which a copolymer of terephthalic acid with a polyethylene glycol is padded on the polyester fiber using an emulsion, containing a 20% concentration of the padding agent, a polyester swelling agent such as benzyl alcohol, and heat. The object of this treatment is to give the basic polyester fiber more hydrophilic character, thereby reducing the tendency of the polyester fiber to retain oily stains.
Other finishing techniques on polyester fabrics can be found in the art. For example, German Patent No. 1,194,363 describes the use of a polyethylene glycol-itaconic acid polymer as an anti-static agent for synthetic fibers to reduce soil pickup. Netherlands Application No. 65/02428 and Belgium Patent No. 641,882 describe the treatment of polyester fibers with polyethylene glycol solutions to increase the hydrophilic character of the fiber. In addition French Patent No. 1,394,401 describes the treatment of a polyester fiber with an alcohol or glycol in the presence of a strong non-volatile acid to increase the hydrophilic character of the fabric.
As can be seen from the prior art hereinbefore described it is well known that fabrics woven from polyester fibers and polyester/cotton fiber blends do not respond the same way during laundering as do typical cotton fabrics. It is well recognized that the problem with polyester and polyester/cotton blends is that because of the hydrophobic character of the fabrics they tend to stain easily with oily soil, and once stained, the oily soil or stain is difficult to remove. In fact it is well known that polyester fabrics tend to be oil scavengers, i.e., they tend to attract soils of an oily nature from the wash water during laundering.
Thus the textile trade has sought to change the inherent characteristics of the polyester fiber either by building into the polyester fiber greater hydrophilic character or by causing the fabric to have greater hydrophilic character through adsorption on the surface of the fiber of materials more hydrophilic in nature than the base polyester fiber. The approaches which have been used heretofore are all involved in the finishing process of the fiber or fabric itself by the fiber or fabric manufacturer and are not associated with the laundering process of the fabric. As a result the treatment received by the polyester fiber or fabric occurs only once and the increase in hydrophilic character is reduced with successive laundering. In some cases the textile finishing process to increase the hydrophilic character of the fabric can be rendered completely ineffective if laundering is done under severe conditions, e.g., in commercial laundries where high pH and high temperature washing conditions are used. Once the hydrophilic characteristics accorded the fiber or fabric have been removed or rendered substantially less effective by subsequent laundering the fabric reverts to its inherent hydrophobic character with the result that oily soils are again very difficult to remove from the fabric.